1. Field of the Invention
The present invention relates to an electronic endoscope apparatus, particularly to a configuration for forming a static image by using a stroboscopic light-emitting mechanism in an apparatus capable of enlarging an observation image by an optical variable-power (magnification) function or the like.
2. Description of the Prior Art
For a recent endoscope, it is proposed to set a variable-power driving mechanism for changing observation distances (varifocal optical system) or focal distances (zoom optical system) to an insertion front end in order to enlarge an observation object picked up by illumination light and drive a movable lens which is a component of the variable-power mechanism. In this case, the torque of a motor is transmitted to a variable-power mechanism by using a linear transmission member such as a multiple-coil-spring member where rotational motion is converted into linear motion to move a predetermined movable lens of an objective optical system forward or backward and execute variable-power operation. Thereby, it is possible to observe an observation object by enlarging it and perform fine diagnosis.
However, though the electronic endoscope apparatus having the variable-power function makes it possible to observe a detailed image of a lesion or the like by enlarging the inside of an observation object by a monitor or the like, there is a problem that the observation object may be blurred. That is, enlarging an observation object represents that blurring due to the pulsation of an observation portion or blurring due to movement of the front end of an endoscope when inserted appears as a large blurring (enlarged and emphasized) even if it is small under standard observation. Particularly when forming and recording a static image, the blurring cannot be ignored.
To decrease the blurring of an observation image, it is considered to raise an electronic shutter speed by controlling the charge storing time of a solid-state image pickup device. However, when increasing the electronic shutter speed while enlarging an observation image, illumination irregularity occurs because the distance between the endoscope front end and the observation object decreases in the case of a varifocal optical system. In the case of a zoom optical system, on the other hand, because the distance between the endoscope front end and the observation object is constant, sufficient illumination light is not applied to the observation object and thereby, exposure deficiency occurs.
The present invention is made to solve the above problems and its object is to provide an electronic endoscope apparatus capable of controlling blurring of an image and forming a preferable static image when picking up an image by using a variable-power mechanism.
To attain the above object, an endoscope apparatus of the present invention includes a solid-state image pickup device for picking up an observation object, an electronic shutter circuit for controlling the charge storing time of the solid-state image pickup device, a stroboscopic light-emitting section for instantaneously emitting stroboscopic light stronger than the illumination light applied to an observation object under normal observation, and a control circuit for setting a shutter speed faster than a shutter speed for a dynamic image by the electronic shutter circuit when a static image is selected by a freeze signal and controlling the stroboscopic light-emitting section so as to emit stroboscopic light.
Moreover, in the case of another aspect of the present invention, an optical variable-power mechanism capable of optically enlarging an observation image by an objective optical system is included and the above control circuit increases the above shutter speed and emits stroboscopic light when a static image is selected while this optical variable-power mechanism is operated.
By setting not only a static-image-forming light source but also a light source used to form a dynamic image to the stroboscopic light-emitting section, it is possible to additionally turn on the static-image-forming light source when the control circuit receives a freeze operation signal. Moreover, it is permitted to set an LED to the front end of an electronic endoscope as the above static-image-forming light source.
According to the above aspect of the present invention, when a freeze button is pressed, a high shutter speed in which exposure time is shorter than that for a dynamic image is set and stroboscopic light is emitted. The stroboscopic light is obtained by instantaneously turning on a light-source lamp at a high voltage or turning on a lamp or an LED added to a stroboscope together with a normal lamp. Thereby, short-time image pickup is realized without causing illumination irregularity or exposure deficiency and it is possible to obtain a clear static image.
According to the above another aspect of the present invention, by driving, for example, a movable lens of an optical variable-power mechanism, it is possible to obtain an observation distance from a wide angle end (Far) up to an enlargement (Near) end and an image in which an observation object is enlarged. Moreover, when a freeze button is pressed and a shutter speed (exposure time) is set to approx. {fraction (1/60)} sec in the standard state in the case of the above shutter speed control, the shutter speed is set so as to be raised as an enlargement rate rises from {fraction (1/500)} sec, {fraction (1/1,000)} sec and . . . while a variable-power function operates and at the same time, stroboscopic light is output. Thereby, because blurring which becomes remarkable in an enlarged static image is controlled, it is possible to obtain an enlarged static image having a preferable quality.